From: Dave Martin <Dave.Martin@arm.com>
To: Andrew Murray <andrew.murray@arm.com>
Cc: Szabolcs Nagy <Szabolcs.Nagy@arm.com>,
Catalin Marinas <Catalin.Marinas@arm.com>, nd <nd@arm.com>,
Will Deacon <Will.Deacon@arm.com>,
"linux-arm-kernel@lists.infradead.org"
<linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCH v2 2/6] arm64: HWCAP: add support for AT_HWCAP2
Date: Thu, 28 Mar 2019 11:27:36 +0000 [thread overview]
Message-ID: <20190328112734.GZ3567@e103592.cambridge.arm.com> (raw)
In-Reply-To: <20190327152414.GF43527@e119886-lin.cambridge.arm.com>
On Wed, Mar 27, 2019 at 03:24:15PM +0000, Andrew Murray wrote:
> On Wed, Mar 27, 2019 at 03:02:25PM +0000, Andrew Murray wrote:
[...]
> > I'll add documentation to Documentation/arm64 to indicate that the upper 32bits
> > of AT_HWCAP will always be 0. Is this correct?
>
> How about this (in Documentation/arm64/elf_hwcaps.txt)?
>
> +
> +
> +4. Unused AT_HWCAP bits
> +-----------------------
> +
> +Each AT_HWCAP and AT_HWCAP2 entry provides for up to 32 hwcaps contained
> +in bits [31:0]. For interoperation with userspace we guarantee that the
> +top bits [63:32] of AT_HWCAP will always be returned as 0.
Since the main reason for reserving bits [63:32] is ILP32, and it's
still unclear when (or if) that will be merged, it feels a bit excessive
to promise that we will never use these bits.
It sounds like glibc has a use for at most one bit in here.
So maybe we can reserve bit 63 (or 32, whatever) and promise that is
zero, but leave the rest uncommitted for now.
Szabolcs, does that sound sensible?
Cheers
---Dave
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next prev parent reply other threads:[~2019-03-28 11:27 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-02-21 12:20 [PATCH v2 0/6] Initial support for CVADP Andrew Murray
2019-02-21 12:20 ` [PATCH v2 1/6] arm64: Handle trapped DC CVADP Andrew Murray
2019-02-21 12:39 ` Mark Rutland
2019-02-21 12:20 ` [PATCH v2 2/6] arm64: HWCAP: add support for AT_HWCAP2 Andrew Murray
2019-02-21 18:45 ` Dave P Martin
2019-02-22 10:35 ` Szabolcs Nagy
2019-03-27 15:02 ` Andrew Murray
2019-03-27 15:24 ` Andrew Murray
2019-03-28 11:27 ` Dave Martin [this message]
2019-03-29 16:44 ` Szabolcs Nagy
2019-03-29 16:57 ` Phil Blundell
2019-04-01 8:14 ` Andrew Murray
2019-03-27 14:53 ` Andrew Murray
2019-03-29 15:39 ` Dave Martin
2019-02-21 12:20 ` [PATCH v2 3/6] arm64: HWCAP: encapsulate elf_hwcap Andrew Murray
2019-02-21 18:45 ` Dave P Martin
2019-03-27 14:03 ` Andrew Murray
2019-03-28 11:32 ` Dave Martin
2019-02-21 12:20 ` [PATCH v2 4/6] arm64: Expose DC CVADP to userspace Andrew Murray
2019-02-21 12:20 ` [PATCH v2 5/6] arm64: add CVADP support to the cache maintenance helper Andrew Murray
2019-02-21 12:20 ` [PATCH v2 6/6] arm64: Advertise ARM64_HAS_DCPODP cpu feature Andrew Murray
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